Generally speaking, the present invention relates to an improvement in a timing mechanism wherein a single cam is axially displaced to permit a cam follower to drop from its outer periphery to engage a switch means, the improvement comprising providing a switch means which includes a pair of movable electrical contact blades having electrical contacts thereon, and dampening means associated with one of the electrical contact blades; and further providing a single cam having a face and an outer periphery, contoured such that the outer periphery is substantially flat and its face has a steep drop with a gentle curvature to permit the cam follower to quickly drop yet remain lightly engaged with the face.
Timing mechanisms are extensively used in the appliance industry to control the functions of an appliance in accordance with a predetermined program. For example, they are extensively used in washers, dryers, dishwashers, and microwave ovens. In some of the applications, the need arises for a short pulsing cycle to be operable within or separate from an overall program. In microwave ovens, for example, such a short pulse is sometimes needed to intermittently apply electrical power to its magnetron. When such power is initially applied to the magnetron, a very high current surge is imposed on the circuit. The surge then drops off. Therefore, there is also a need in this application to provide an even shorter pulse whereby current can be initially switched through a current limiting resistor.
In U.S. Pat. No. 4,246,454 there is described a timing mechanism employing an axial movable cam with two cam followers that opens and closes two switches. While the mechanism very admirably satisfies the above-noted needs, it would be far better from an economic viewpoint if the surge problem could be met by using only one switch. In order to use just one switch, one of the main problems that needs to be overcome is that of the closure mechanism causing contact bounce. Contact bounce causes contact deterioration through double arcing as well as "timer hangup". The present invention admirably solves this problem.